Hemant's Blog

FUNCTIONAL REQUIREMENTS - Display top 10 users on the leaderboard Show user's specific rank Display users who are 4 places up and 4 places down below the user NON-FUNCTIONAL REQUIREMENTS - Real-time update on scores Score update is reflected on the leaderboard in real-time Scalability, Availability and Reliability API SIGNATURE - POST /v1/scores                (update score on the leaderboard) GET /v1/scores                  (fetch top 10 users with their scores) GET /v1/scores/{userdId} (get the user rank on the leaderboard) DATA MODEL - We can use a RDBMS solution for this problem. Whenever a user wins a match we update the score of the user by 1, but the main problem arises when we have to fetch the ranks of user/top 10 user.  We cannot sort millions of rows in the DB for every request. One optimisation we could do is to add an index and limit the results, but this also requires a full scan of t...

 We need to design a booking system like booking.com/airbnb. First we look at the requirements: FUNCTIONAL REQUIREMENTS: Hotel- Onboarding Updates See the booking details User- Search hotels Book rooms  Check bookings Analytics Dynamic pricing NON-FUNCTIONAL REQUIREMENTS: Moderate latency - It's ideal to have low latency when user makes a reservation, but it's acceptable if the system takes a few seconds to book the same room, High Availability High Consistency High Scalability API Signatures: We'll have basic CRUD service (Create, Read, Update, Delete) Hotel-related APIs: GET /v1/hotels/ID POST  /v1/hotels PUT  /v1/hotels/ID DELETE  /v1/hotels/ID  Room-related APIs: GET  /v1/hotels/ID/rooms/ID POST  /v1/hotels/ID/rooms PUT  /v1/hotels/ID/rooms/ID DELETE  /v1/hotels/ID /rooms/ID Reservation-related APIs: GET  /v1/reservations (get reservation history) GET  /v1/reservations/ID (detailed information about a reservation) POST...

 To design a notification system we first understand the different third party services. How do these third-party services work? Third Party Services: A provider builds and sends notification request to the required third part service. The provider provides the third-party service with device token and the payload.   Gathering Contact Information:   To send notifications, we need to gather device tokens, phone numbers, or email addresses. To do this, when a user installs our application or signs up for the first time, API servers collect the user contact info and store them in the database. FUNCTIONAL REQUIREMENTS:   Should be able to send notifications. Pluggable: Should be extensible to send different types of notification. SaaS – Should be built as SaaS product with rate limiting even it is a internal tool. Because we should limit the number of requests from a service. Prioritization – We must send notifications on bases of priority, as OTP is high priority wherea...

Problem Statement -  There are 100 doors in a row, all doors are initially closed. A person walks through all doors multiple times and toggle (if open then close, if close then open) them in the following way:  In the first walk, the person toggles every door  In the second walk, the person toggles every second door, i.e., 2 nd , 4 th , 6 th , 8 th , …  In the third walk, the person toggles every third door, i.e. 3 rd , 6 th , 9 th , …  Likewise, In the 100 th  walk, the person toggles the 100 th  door.  Which doors are open in the end?   Solution -  Approach - We'll try to solve this question mathematically First we understand that each door state will be changed, depending on its number of factors and to be closed at the end the number of factors of that particular number should be odd. For eg:- Door 1 will be open at end as its only factor is 1 (odd), Door 2 will be closed as it has factors 1&2 (even). Now, let us consider a numb...